optimization/7427: gcc-3.1.1 -O2 problem for checksum calculation (powerpc)
makoto@ki.nu
makoto@ki.nu
Sun Jul 28 15:26:00 GMT 2002
>Number: 7427
>Category: optimization
>Synopsis: (powerpc) -O2 problem for checksum calc.
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: wrong-code
>Submitter-Id: net
>Arrival-Date: Sun Jul 28 15:26:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator: Makoto Fujiwara
>Release: 3.1.1
>Organization:
office.ki.nu
>Environment:
System: NetBSD quick 1.5ZC NetBSD 1.5ZC (GENERIC) #0: Fri Mar 29 19:38:39 JST 2002 tsubai@mahoro:/a/0328/src/sys/arch/macppc/compile/GENERIC macppc
host: powerpc--netbsd
build: powerpc--netbsd
target: powerpc--netbsd
configured with:../configure --with-gcc-version-trigger=/export/local-src/gcc-3.1.1/gcc/version.c --host=powerpc-unknown-netbsd1.5ZC --norecursion
>Description:
With code attached, say, sum.c, the output with -O2 shows different value with -O or -O1.
-O sum = 0x68ac
-O1 sum = 0x68ac
-O2 sum = 0x8fb9
>How-To-Repeat:
Compile following file on macppc machine with -O1 and -O2 and execute them respectively.
-------------------------------
#include <stdio.h>
struct buf {
int data;
};
bug(m)
struct buf *m;
{
int sum = 0;
struct buf tmp;
unsigned short *w = (void *)&tmp;
bzero(&tmp, sizeof tmp);
tmp.data = m->data;
//asm volatile ("" ::: "memory");
sum += w[0];
sum += w[1];
printf("sum = 0x%x\n", sum);
return 0;
}
main()
{
struct buf m;
m.data = 0x12345678;
bug(&m);
}
-------------------------------
I will attach the .s code for the reference:
(1) with -O1
.........................................................................
.file "sum.c"
.section .rodata
.align 2
.LC0:
.string "sum = 0x%x\n"
.section ".text"
.align 2
.globl bug
.type bug,@function
bug:
stwu 1,-16(1)
mflr 0
stw 0,20(1)
lwz 0,0(3)
stw 0,8(1)
lhz 4,8(1)
lhz 0,10(1)
add 4,4,0
lis 3,.LC0@ha
la 3,.LC0@l(3)
crxor 6,6,6
bl printf
li 3,0
lwz 0,20(1)
mtlr 0
addi 1,1,16
blr
.Lfe1:
.size bug,.Lfe1-bug
.align 2
.globl main
.type main,@function
main:
stwu 1,-16(1)
mflr 0
stw 0,20(1)
lis 0,0x1234
ori 0,0,22136
stw 0,8(1)
addi 3,1,8
crxor 6,6,6
bl bug
lwz 0,20(1)
mtlr 0
addi 1,1,16
blr
.Lfe2:
.size main,.Lfe2-main
.ident "GCC: (GNU) 3.1.1"
.........................................................................
(2) with -O2
.........................................................................
.file "sum.c"
.section .rodata
.align 2
.LC0:
.string "sum = 0x%x\n"
.section ".text"
.align 2
.globl bug
.type bug,@function
bug:
stwu 1,-16(1)
mflr 0
stw 0,20(1)
lhz 4,8(1)
lhz 0,10(1)
lwz 9,0(3)
lis 3,.LC0@ha
add 4,4,0
la 3,.LC0@l(3)
stw 9,8(1)
crxor 6,6,6
bl printf
lwz 0,20(1)
li 3,0
addi 1,1,16
mtlr 0
blr
.Lfe1:
.size bug,.Lfe1-bug
.align 2
.globl main
.type main,@function
main:
stwu 1,-16(1)
mflr 0
stw 0,20(1)
addi 3,1,8
lis 0,0x1234
ori 0,0,22136
stw 0,8(1)
crxor 6,6,6
bl bug
lwz 0,20(1)
addi 1,1,16
mtlr 0
blr
.Lfe2:
.size main,.Lfe2-main
.ident "GCC: (GNU) 3.1.1"
.........................................................................
>Fix:
Not known at the moment.
>Release-Note:
>Audit-Trail:
>Unformatted:
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